Does AV prevent extremist politics?

Mostly; extremist parties are able to get elected under FPTP because they can take advantage of minority election.

Under AV, any candidate who wants to win must get a true majority and broad support from the voters in an election. Extremist parties are called that because their views are far outside most people’s opinions, and unlikely to be supported by more than 50% of voters.

It’s telling that, although the NO campaign claims that AV encourages extremism, the BNP are dead-set against AV…